1. Technical Field
The present invention relates to a plug component (artificial bone prosthetic material) for use in surgery required to plug a bone tunnel, such as anterior cruciate ligament reconstruction or bone biopsy. The present invention relates to a material for filling bone tunnels of humans or animals, more specifically to a material for filling bone tunnels formed in surgery on ligaments or tendons.
2. Description of the Related Art
Ligaments and tendons are fibrous tissues attached to bones and perform the functions of transmitting mechanical tensile forces, preventing dislocation, guiding joint movement, and acting to transmit muscle forces. However, ligaments or tendons are liable to sustain damage when a heavy load is applied to the knee by injury during sports such as basketball, soccer, handball, volleyball, football, snowboarding, and skiing, traffic injury, work accident, daily movements or the like. Damage to ligaments or tendons lead to joint pain and restriction of physical activity, and ligaments or tendons are less likely to spontaneously recover. Therefore, damage that does not heal by conservative therapy has been conventionally treated by surgery such as ligament reconstruction, ligament repair, syndesmoplasty, tendon reconstruction, tendon repair, or tendinoplasty. If anterior cruciate ligament (ACL) damage is left untreated, hematoma or swelling occurs within the knee joint to reduce stability of the knee. In this case, there is a risk of damage to the meniscus, joint capsule or the like and various symptoms occur (for example, the knee suddenly buckles). If ligament damage is left untreated for a long time, there is a case where joint cartilage is damaged and knee tissue damage becomes irreparable, which may lead to osteoarthritis, in which the knee joint does not normally function. Therefore, ACL reconstruction needs to be performed as soon as possible.
In these surgeries, tunnels are formed in bone, and a ligament or tendon graft material is inserted into the bone tunnels and fixed. After surgery, the graft material is biologically fixed in the bone tunnels to heal. Specifically, ACL reconstruction is performed in the following method. A bone tunnel is drilled in the medial side of the tibia. A torn tendon is reconstructed. It is to be noted that there are two methods for ligament reconstruction. One is a BTB (bone-patellar tendon-bone) method using a patellar tendon auto-graft and the other is a STG method using tendons harvested from the semitendinosus tendon and the gracilis tendon located on the medial and posterior side of the knee. In some cases, an artificial tendon is used. Strings are tied to both ends of a reconstruction ligament, and the reconstruction ligament is passed through the bone tunnels by passing the string through the bone tunnels from the tibial side by pulling the string from the femur side. After the string is passed through the bone tunnels, fixation is achieved on the femur side by an endobutton. The string tied to the reconstructed tendon is pulled while the degree of flexion of the knee is checked to determine the degree of tension to fix the string to the medial side of the tibia. The string emerging from the tibial tunnel is fixed by a screw and a small plate. In this case, the tibial tunnel is not completely filled with the graft material and a defect often remains in the tibial tunnel.
However, when a defect remains in a bone tunnel, it takes a long time to fill the defect with regenerated bone after surgery, or hemorrhage from exposed bone marrow in the bone tunnel causes problems after surgery. Further, the defect remaining in the bone tunnel or blood pooled in the defect has risks such as infection. Moreover, when a reconstruction ligament or tendon is torn again and a second surgery needs to be performed, there is a case where the defect remaining in the bone tunnel becomes a problem to the second surgery.
As a solution to these problems, there is a method for filling a bone tunnel with bone wax or an autologous bone or bone substitute. However, in the case of using bone wax, the postoperative course is not satisfactory and there is also a case where infection or swelling occurs or a tumor occurs. Further, bone wax often serves as a source of infection, and when once infection occurs, bone wax needs to be removed. Moreover, bone wax has the drawback of interfering with bone fusion. There is also a drawback that an autograft needs to be harvested from another part of the body. A bone substitute has been developed as a material for filling a bone defect to promote bone regeneration without injury autologous bone in another part of the body. It is preferable that such a bone substitute has a shape or structure that fits a bone tunnel formed in surgery on ligaments or tendons.
However, it is hard to say that conventional artificial bone prosthetic materials have a shape or structure that fits a bone tunnel. The problems associated with a defect remaining in a bone tunnel cannot be solved when the bone tunnel is filled with a material whose shape or structure does not fit the bone tunnel.
For example, JP-A-2002-272756 discloses a fixing instrument for fixing a reconstruction ligament to a tibia side. However, in such a fixing instrument, a bone tunnel is not satisfactorily plugged.
As described above, ACL reconstruction is performed by transplanting and fixing a reconstruction ligament in bone tunnels formed in the tibia and the femur. However, the bone tunnel is not completely filled with the reconstruction ligament and there is a space left in the bone tunnel. A space remaining in a bone tunnel causes the following problems.
(1) Subcutaneous hemorrhage, pain, and swelling occur due to bleeding from bone marrow in a bone tunnel, and therefore the risk of infection increases.
(2) There has been reported that the incidence of a tendon re-tear after ACL reconstruction is 5 to 10%. A bone tunnel formed in surgery for a first ACL reconstruction becomes an obstacle to surgery for a second ACL reconstruction. When a re-reconstruction is performed, surgery for the second ACL reconstruction needs to be performed in two time periods. First, surgery for transplanting an autologous bone harvested from, for example, an ilium into a bone tunnel formed in surgery for a first ACL reconstruction is performed depending on cases. Then, after the completion of bone fusion, surgery for the second ACL reconstruction is performed. Heavy mental, physical, and economic burdens are placed on a patient.
According to the catalog of NEOBONE®, it is disclosed that when a hydroxyapatite bone substitute having interconnected pores is transplanted into a bone defect, the bone defect is quickly filled with a regenerated bone after transplantation.
According to the catalog of NEOBONE® X, it is disclosed that NEOBONE® X is a combination of hydroxyapatite having interconnected pores and a solid part of hydroxyapatite, and therefore achieves both an increase in strength and induction of bone regeneration.
However, it cannot be said that NEOBONE® and NEOBOEN® X have a shape or structure that optimally fits a bone tunnel formed in surgery on ligaments or tendons. Bone in which bone tunnels are formed in surgery on ligaments or tendons has a structure in which spongy bone that contains bone marrow and is rich in cellular elements is surrounded by a bone cortex having high strength. Therefore, a bone prosthetic material needs to have morphology and strength similar to the structure of the bone. Further, the use of a bone prosthetic material having size, length, and shape that fit a bone tunnel is advantageous for regeneration or repair of bone in a living body.